October 20, 2009

Stature evolution in Andaman Islanders

CURRENT ANTHROPOLOGY Volume 50, Number 5, October 2009DOI: 10.1086/605429

Stature, Mortality, and Life History among Indigenous Populations of the Andaman Islands, 1871–1986

J. T. Stock and A. B. Migliano

Despite considerable interest in the evolution of small body size, there is little evidence for changes in body size within small‐bodied human populations. This study combines anthropometric data from a number of studies of the body size of Andaman Islanders from 1871 to 1986. The colonial history of the Andaman Islands is characterized by high rates of mortality among the indigenous populations. However, long‐term conflicts between tribal groups of the Andaman Islands and British and Indian settlers led to some groups being relatively isolated and sheltered from infectious disease and the high rates of mortality that affected other groups. When temporal trends in stature are compared in this context, there is evidence for a reduction in stature among the Great Andamanese who had close contact with the British during the period of highest mortality. Adult stature among the Onge appears to have increased as government involvement diminished following Indian independence. The Jarawa, who had lower rates of mortality throughout the past century, have significantly higher stature than the other groups. These results are interpreted in the context of life‐history theory, adaptation, and plasticity. They provide the first long‐term diachronic evidence for a relationship between mortality and stature among small‐bodied humans.

8 comments:

The article follows in the footsteps of Migliano et al. 2007 who proposed that stature reduction in pygmy population is a by-product of selection for early onset of reproduction in the context of high mortality rates. Both articles effectively challenge an old view that pygmies throughout the world constitute relics of an original population subsequently marginalized by the incoming Mongoloids and Negroids. In fact, whether African Pygmies and African Bushmen, Andaman islanders and the Aeta of the Philippines, all these cases of small stature in human populations are independent accidents of history. It's also likely that these accidents of history happened not too long ago, as the recent linguistic research into the genetic connection between Austronesian-speakers and certain Andaman languages illustrates.

The shrinkage has nothing to do with the race or the humans or even their species, Homo sapiens. It happens quite often when animals are stranded on islands with limited biodiversity and carrying capacity.

In Mediterranean Europe there are examples of large animals reducing in stature and mass e.g Elephants, that were stranded on Mediterranean islands due to sea level rise from mainland Europe or Africa. There are almost animals known for small stature and mass that have dramically increases in size under the same conditions e.g Dormouse species.

As far as longevity is concerned, it is well known that large animals have slower metabolisms, take longer to reach breeding maturity and live longer. Small animals like Mice have high metabolisms, breed earlier and have very short longevities.

The Andaman Islanders while they are isolated and also eschew contact with outsiders, are being looked after by the Indian Government who restrict contact with them thereby reducing disease risks and provide them with outside food sources the islander do not hunt or gather on the islands. It is hardly surprising that outside contact with outside diseases and the artificial feeding of islander may contribute to changes in stature and longevity.

"the recent linguistic research into the genetic connection between Austronesian-speakers and certain Andaman languages illustrates".

Have you got a link for that? I was under the impression that the Andaman languages were lumped with the Indo-Pacific languages of New Guinea, although that grouping is rather a catchall collection rather than being an identified family.

This research by Juliette Blevins from Max-Planck was published in Oceanic Linguistics. It's available online at

email.eva.mpg.de/~blevins/pdf/webpub2007a.pdf

Also, a press release by Comrie:

www.eva.mpg.de/english/press/PMs.../PM_Andaman_english.pdf

I found the evidence solid, especially thanks to the parallelism in grammatical forms (inalienable possession markers in Ongan and their apparent traces in proto-Austronesian in the form of otherwise-meaningless add-ons to the onset of certain words).

I'm not sure what this new connection does to the out-of-Taiwan hypothesis but probably it makes an Austronesian homeland in south China more plausible than on an island.

Just had another thought: the Ongan-Austronesian connection reinforces the pattern by which populations with small stature tend not to have their own language. African Pygmies speak the languages of their Niger-Congo and Nilo-Saharan neighbors, Aeta in the Philippines speak an Austronesian language (Botolan). This points to the relative recency of the small-stature populations and to the fact that they didn't adopt a different language but are closely related genetically to populations with normal size who speak the languages of the same language stock. Long mtDNA and Y-DNA lineages of the African Pygmies may therefore be result of a demographic process, and not an automatic indication of age.

"I'm not sure what this new connection does to the out-of-Taiwan hypothesis".

Probably doesn't change it much. The language(s, I haven't looked at the links yet) may have reached the Andamans after humans first arrived there. Alternatively humans may have reached the islands even more recently than I have proposed. There is ceertainly no evidence that they reached the Andamans before a little more than 10k.

Ongan is reconstructed by Blevins as an outgroup to Austronesian as a whole including its Taiwanese branches. Andamanese don't show 9 bp deletion lineages, which doesn't mean much as these lineages have a very spotty distribution and haven't been detected in ancient Lapita samples either. With the inclusion of Tai-Kadai into the mix, the situation is a bit messy. But the overall picture of a large-scale population movement from South China eastward, southward and westward seems to be clear.

"With the inclusion of Tai-Kadai into the mix, the situation is a bit messy".

Tai-Kadai is also often claimed to be some relation to Austronesian so that may put Ongan even more distant. And then we run into the possible relationship of the Munda languages to Austronesian. It would make sense if Ongan was part of the Munda expansion from SE Asia.

You may be interested in my essay on the subject of Polynesian origins. I have grouped the Munda languages into Nahali and you'll see that the diagram fits the connection claimed in the articles you've linked. I postulate an ultimate connection of Austronesian to the Na-Dene languages of North America, which may fit with your ideas:

"But the overall picture of a large-scale population movement from South China eastward, southward and westward seems to be clear".

My contribution, where I suggest much the same: Thai-Kadai and Austroasiatic languages by land and Austronesian languages by sea. Obviously the situation is far more complicated than I have managed to piece together:

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